This invention relates generally to pneumatically operated lifting devices and, more particularly, to low profile, portable air jacks used primarily in vehicle service stations, garages and repair shops to raise one end of a vehicle.
Such low profile jacks are widely used in auto shops because they can be readily moved about and properly positioned beneath a vehicle to be lifted regardless of the space available beneath the vehicle.
The use of pressurized air to operate such low profile jacks is very desirable, since most vehicle shops already have pressurized air systems.
It is also desirable that these low profile air jacks be of compact and simple construction, within the design limitations of the air pressure available, weight to be lifted, height to which lifted, and the low profile requirements.
In a known simple design of a low profile air jack, the vehicle is raised by a lifting member, which is pivotably attached to the top side of the jack frame, by application of a force against a downwardly-extending lever arm of this lifting member. The force required is produced by a horizontally disposed air cylinder mounted in the jack frame. The low profile requirement limits the length of the lever arm, the diameter of the air cylinder, and angular displacement of the lifting member, which, in turn, determines the length of the lifting member required to achieve the desired elevation of the vehicle.
The weight-lifting capability of such a low profile air jack is limited by the pressure of the available air supply. To increase the weight-lifting capability of this jack, the force applied to the lever arm can be increased above that which would be applied by a single, directly coupled air cylinder.
One method of increasing the force applied to the lever arm of the lifting member is disclosed in U.S. Pat. No. 3,664,635, issued May 23, 1972, to Mr. Gary L. Kincaid. This is achieved by the use of several air cylinders, whose pistons are attached to a common piston shaft, which, in turn, is directly coupled to the lever arm of the lifting member by a rigid connecting link.